Distortion correction for projector

ABSTRACT

An image processing device for a projector including an image formation section that emits light of an image, and a projection system that projects the emitted light onto a projection surface. The image processing device includes: a target display area determination section that determines, in a display area serving as a reference on the projection surface, based on a current value of a parameter, any of target display areas set for values possibly taken by the parameter within an allowable range to be targeted on a distortion-free image for display on the projection surface; a reference formation area determination section that determines, corresponding to the reference display area, based on information about a projection angle of the projector with respect to the projection surface, a reference formation area to be formed with a virtual distorted image that is supposed to be formed in the image formation section when the distortion-free image is displayed in the reference display area; and a correction application section that generates corrected image data for supply to the image formation section by correcting any provided original image data to form a target distorted image in a target formation area, which corresponds to the target display area as is defined by a relationship between the reference display area and the reference formation area, and is formed with the target distorted image that is supposed to be formed in the image formation section when the distortion-free image is displayed in the reference display area.

BACKGROUND

1. Technical Field

The present invention relates to image processing for projectors and,more specifically, to a distortion correction technique for images to bedisplayed on projection surfaces.

2. Related Art

Projectors generally display images from a low angle onto projectionsurfaces. With such low-angle image projection, the resulting imagesdisplayed on the projection surfaces suffer from distortion. For thisreason, in a projector of Patent Document 1 (JP-A-2002-72351), anydistorted image is formed in an internally-provided image formationsection exemplified by a liquid crystal light valve so that theresulting image to be displayed on the projection surface becomes freefrom distortion. Note here that the low-angle image projection denotesthe projection technique in which the light source optical axis of aprojector is not vertical to a projection surface.

With such a previously-known technique, however, there still remains adifficulty in correcting image distortion with accuracy for display onthe projection surface.

For distortion correction of images for display on projection surfaces,there originally needs to give consideration to image display areas onthe projection surfaces, more specifically, to image display positionsand sizes on the projection surfaces. The determination factor for theimage display areas is the shift and zoom positions of a projectionsystem, the position and magnification of distorted images to be formedin an image formation section, and the like. However, no considerationhas been given to such image display areas, and in Patent Document 1,there is indeed a description of changing the shape of an image formedon a liquid crystal panel depending on the position of a projectionlens, but there is no disclosure about the specific technique of makingsuch changes.

SUMMARY

An advantage of some aspects of the invention is to accurately correctany distortion observed in images to be displayed on projectionsurfaces.

A first aspect of the invention is directed to an image processingdevice for a projector including an image formation section that emitslight of an image, and a projection system that projects the emittedlight onto a projection surface. The image processing device includes: atarget display area determination section that determines, in a displayarea serving as a reference on the projection surface, based on acurrent value of a parameter, any of target display areas set for valuespossibly taken by the parameter within an allowable range to be targetedon a distortion-free image for display on the projection surface; areference formation area determination section that determines,corresponding to the reference display area, based on information abouta projection angle of the projector with respect to the projectionsurface, a reference formation area to be formed with a virtualdistorted image that is supposed to be formed in the image formationsection when the distortion-free image is displayed in the referencedisplay area; and a correction application section that generatescorrected image data for supply to the image formation section bycorrecting any provided original image data to form a target distortedimage in a target formation area, which corresponds to the targetdisplay area as is defined by the relationship between the referencedisplay area and the reference formation area, and is formed with thetarget distorted image that is supposed to be formed in the imageformation section when the distortion-free image is displayed in thetarget display area.

With such an image processing device of the first aspect, any originalimage data is so corrected that a target distorted image is formed in atarget formation area, which is defined by the relationship between areference display area and a reference formation area, and thegeneration result is corrected image data. That is, in this imageprocessing device, the corrected image data is generated withconsideration given to the target display area that is determined basedon the current value of a parameter so that any distortion observed inimages can be corrected with accuracy for display on a projectionsurface.

In the image processing device of the first aspect, the parameterpreferably includes the shift position of the projection systemindicating the layout of the projection system in a direction orthogonalto an axis passing through the center of an image formation surface ofthe image formation section.

When the shift position of the projection system is changed, the targetdisplay area is also changed in position. Accordingly, by the parameterincluding the shift position of the projection system as above, thecorrected image data can be generated with consideration given to thetarget display area corresponding to the shift position of theprojection system.

In the image processing device of the first aspect, the parameterpreferably includes the zoom position of the projection systemindicating the layout of the projection system in a direction parallelto an axis passing through the center of an image formation surface ofthe image formation section.

When the zoom position of the projection system is changed, the targetdisplay area is also changed in position. Accordingly, by the parameterincluding the zoom position of the projection system as above, thecorrected image data can be generated with consideration given to thetarget display area corresponding to the zoom position of the projectionsystem.

The image processing device of the first aspect may further include atarget formation area determination section that determines the targetformation area corresponding to the target display area based on therelationship between the reference display area and the referenceformation area.

In the image processing device of the first aspect, when the targetformation area does not fit in the image formation section, the targetformation area determination section changes the position of the targetdisplay area to ensure a fit in the image formation section, and basedon the relationship between the reference display area and the referenceformation area, newly determines the target formation area correspondingto the target display area after the position change.

Alternatively, in the image processing device of the first aspect, theprojector may further include an actuator for changing the shiftposition of the projection system. When the target formation area doesnot fit in the image formation section, the target formation areadetermination section may change the position of the target formationarea to ensure a fit in the image formation section, and make theactuator change the shift position of the projection system to ensure animage display in the target display area.

When the target formation area does not fit in the image formationsection, the resulting image is not fully displayed on the projectionsurface. With the above being the case, however, the resulting image canbe fully displayed on the projection surface, and any distortionobserved in the image can be corrected with accuracy for display on theprojection surface.

In the image processing device of the first aspect, the parameterpreferably includes the position of the target distorted image that issupposed to be formed in the image formation section.

When the target distorted image to be formed in the image formationsection is changed in position, the target display area is also changed.Accordingly, by the parameter including the position of the targetdistorted image as above, the corrected image data can be generated withconsideration given to the target display area corresponding to theposition of the target distorted image in the image formation section.

In the image processing device of the first aspect, the parameterpreferably includes the magnification of the target distorted image thatis supposed to be formed in the image formation section.

When the target distorted image to be formed in the image formationsection is changed in magnification, the target display area is alsochanged. Accordingly, by the parameter including the magnification ofthe target distorted image as above, the corrected image data can begenerated with consideration given to the target display areacorresponding to the magnification of the target distorted image in theimage formation section.

Note here that the invention can be embodied in various forms, includingan image processing device and method, a projector equipped with theimage processing device and an image processing method therefor, acomputer program for implementing functions of an image processingdevice, a recording medium recorded with the computer program,computer-programmed data signals embodied in carriers, and others.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a block diagram showing the configuration of a projector PJ ina first embodiment.

FIGS. 2A and 2B are each an illustrative diagram showing a projectionangle of the projector PJ.

FIGS. 3A and 3B are illustrative diagrams showing, respectively, animage formed on a liquid crystal light valve, and an image displayed ona screen based on the shift position of a projection system.

FIGS. 4A and 4B are illustrative diagrams showing, respectively, animage formed on the liquid crystal light valve, and an image displayedon the screen based on the zoom position of the projection system.

FIG. 5 is a flowchart showing the procedure of correcting any distortionobserved in an image displayed on the screen.

FIG. 6 is an illustrative diagram showing a target display area Wst.

FIG. 7 is an illustrative diagram showing a reference formation areaWLs.

FIGS. 8A and 8B are illustrative diagrams showing, respectively, areference display area WSs and the reference formation area WLs.

FIGS. 9A and 9B are illustrative diagrams showing, respectively, thetarget display area WSt and a target formation area WLt.

FIGS. 10A and 10B are each an illustrative diagram showing a processwhen the target formation area fits in the liquid crystal light valve.

FIGS. 11A-1 to 11B-2 are each an illustrative diagram showing a firstprocess when the target formation area does not fit in the liquidcrystal light valve.

FIGS. 12A-1 to 12B-2 are each an illustrative diagram showing a secondprocess when the target formation area does not fit in the liquidcrystal light valve.

FIG. 13 is a block diagram showing the configuration of a projector PJBin a second embodiment.

FIGS. 14A and 14B are illustrative diagrams showing, respectively, animage formed on a liquid crystal light valve, and an image displayed ona screen based on the position of the image.

FIGS. 15A and 15B are illustrative diagrams showing, respectively, animage formed on the liquid crystal light valve, and an image displayedon the screen based on the magnification of the image.

FIG. 16 is a flowchart showing the procedure of correcting anydistortion observed in an image displayed on the screen.

FIG. 17 is an illustrative diagram showing a target display area WSBt.

FIG. 18 is an illustrative diagram showing a reference formation areaWLBs.

FIGS. 19A and 19B are illustrative diagrams showing, respectively, thetarget display area WSBt and a target formation area WLBt.

DESCRIPTION OF EXEMPLARY EMBODIMENTS A. First Embodiment

A-1. Configuration of Projector

FIG. 1 is a block diagram showing the configuration of a projector PJ ina first embodiment. The projector PJ is configured to include anillumination system 100, a liquid crystal light valve 300, and aprojection system 340. In FIG. 1, the optical system is shown quitesimplified.

The projector PJ also includes a light source lamp drive section 110, aliquid crystal light valve drive section 310, a projection systemadjustment section 350, a shift position detection section 362, a zoomposition detection section 364, a CPU (Central Processing Unit) 400, animage input section 410, an image processing section 420, an operationsection 510, and a remote control interface (IF) section 520. The CPU400 is in charge of exercising control over the projector.

The light source lamp drive section 110 drives a light source lampincluded in the illumination system 100. The liquid crystal light valvedrive section 310 drives the liquid crystal light valve 300 inaccordance with image data coming from the image processing section 420.

The projection system adjustment section 350 is equipped with a motor,and adjusts the position of the projection system 340. Morespecifically, the projection system adjustment section 350 moves thelens of the projection system in the direction orthogonal to the lightsource optical axis LA so that the projection system is adjusted byshift position. The projection system adjustment section 350 also movesthe lens of the projection system in the direction parallel to the lightsource optical axis LA so that the projection system is adjusted by zoomposition. Note that the light source optical axis denotes the centeraxis of light coming from the illumination system 100, and the lightsource optical axis passes through the center of an effective displayarea (image formation surface) of the liquid crystal light valve 300.

The shift position detection section 362 detects the shift position ofthe projection system. The zoom position detection section 364 detectsthe zoom position of the projection system. Note here that as the shiftposition detection section and the zoom position detection section, anywell-known position detection means can serve well, e.g., rotaryencoder, or variable resistor.

The image input section 410 supplies any externally-provided image datato the image processing section 420. For example, the image inputsection 410 receives an RGB signal provided by a computer, a compositesignal provided by a video recorder, and the like, and supplies imagedata to the image processing section 420. The image input section 410reads image data stored in a memory card MC for supply to the imageprocessing section 420.

The image processing section 420 processes the image data provided bythe image input section 410, and the generation result is processedimage data. The image processing section 420 supplies the processedimage data to the liquid crystal light valve drive section 310.

The image processing section 420 specifically includes a computerprogram serving as the distortion correction section 430. The distortioncorrection section 430 is configured to include a target display areadetermination section 432, a reference formation area determinationsection 434, a target formation area determination section 436, and acorrection application section 438. The distortion correction section430 functions by the CPU 400 executing the computer program. Note herethat the computer program is distributed in a computer-readablerecording medium such as CD-ROM.

As described above, when low-angle image projection is made on thescreen, the image formed on the liquid crystal light valve 300 has nodistortion but the image displayed on the screen suffers fromsubstantially-trapezoidal distortion. On the other hand, if asubstantially-trapezoidal distorted image is formed on the liquidcrystal light valve 300, the resulting image on the screen becomes freefrom distortion, i.e., rectangular image of a correct aspect ratio. Sucha rectangular image is hereinafter simply referred also to as regularimage. The distortion correction section 430 corrects the original imagedata, and the generation result is corrected image data representing adistorted image. In accordance with the corrected image data, adistorted image is formed on the liquid crystal light valve 300 so thata regular image is displayed on the screen.

The operation section 510 makes the CPU 400 execute various types ofprocesses in response to the user's operation. For example, throughoperation of the operation section 510, a user can display a menu screenon the screen. By following the menu screen, the user can make varioustypes of settings such as image contrast.

Similarly to the operation section 510, the remote control IF section520 makes the CPU 400 execute various types of processes in response tothe user's operation of a remote controller RC.

A-2. Image Distortion on Screen Display

FIGS. 2A and 2B are each an illustrative diagram showing therelationship between the projector PJ and a screen SC. In FIGS. 2A and2B, the screen SC is disposed along the xy plane, and the projector PJis assumed to radiate light toward the side of z of the screen. As shownin FIG. 2A, the tilt angle of the projector PJ is represented by anangle φ, formed by the normal n of the screen SC and the light sourceoptical axis LA of the projector. As shown in FIG. 2B, the pan angle ofthe projector PJ is represented by an angle θ, formed by the normal n ofthe screen SC and the light source optical axis LA of the projector.When the tilt angle φ or the pan angle θ is not 0 degree, the low-angleimage projection is implemented.

Some type of projector is designed to realize the low-angle imageprojection in the initial state. More specifically, a significant tiltangle φi is sometimes set in the initial state of some type ofprojector. With this being the case, the tilt angle φ of FIG. 2A is,actually, represented by the sum of the angle φi in the initial stateand a user-set angle φu. Herein, the angle φu is user-changeable throughadjustment of the leg height of the projector, for example.

When the low-angle image projection is made onto a screen, if adistorted image is formed on a liquid crystal light valve before aprojection system is changed in position for the purpose of displaying aregular image on the screen, i.e., before the shift and zoom positionsof the projection system are changed, the resulting image on the screenis distorted. This is caused because the image display area on thescreen is changed as the projection system is changed in position.

FIGS. 3A and 3B are illustrative diagrams showing, respectively, animage formed on a liquid crystal light valve, and an image displayed ona screen based on the shift position of a projection system.

Considered here is a case where the shift position of the projectionsystem 340 is located at the center, more specifically, a case where theshift position is so set that the light source optical axis coincideswith the center axis of the projection system 340. In such a case, whenthe liquid crystal light valve 300 is formed with a trapezoidaldistorted image LP1 of FIG. 3A, the screen displays an image SP1 of FIG.3B.

If no change is made to the distorted image LP1 formed on the liquidcrystal valve 300 before the projection system 340 is changed in shiftposition, as shown in FIG. 3B, images SP1 a to SP1 d on the screen areall changed in position. As a result, the images SP1 a to SP1 d are allchanged in shape. For example, when the shift position of the projectionsystem is moved toward the right, in other words, when the imageposition on the screen is moved toward the right, the screen displaysthe distorted image SP1 a extending to the right.

FIGS. 4A and 4B are illustrative diagrams showing, respectively, animage formed on a liquid crystal light valve, and an image displayed ona screen based on the zoom position of a projection system.

Considered here is a case where the zoom position of the projectionsystem is located at an in-between position, more specifically, when thezoom position is located at between the wide-side and the tele-side. Insuch a case, when the liquid crystal light valve 300 is formed with atrapezoidal distorted image LP2 of FIG. 4A, the screen displays an imageSP2 of FIG. 4B.

If no change is made to the distorted image LP2 formed to the liquidcrystal valve 300 before the projection system 340 is changed in zoomposition, as shown in FIG. 4B, images SP2 a to SP2 b on the screen areboth changed in position. As a result, the images SP2 a and SP2 b areboth changed in shape. For example, when the zoom position of theprojection system is moved toward the wide-side, in other words, whenthe image size is increased for display on the screen, the screendisplays the distorted image SP2 a expanding upward.

As such, when the image display area on the screen is changed as theshift and/or zoom positions of the projection system are changed, theimage displayed on the screen is changed in shape.

The issue here is that, when the distorted image is determined by shapefor formation onto the liquid crystal light valve, no consideration hasbeen given to the shift and zoom positions of the projection system. Inother words, previously, the image display area on the screen has notbeen considered. Therefore, it has been difficult to display on thescreen rectangular images (regular images) of a correct aspect ratio.

In consideration thereof, in the embodiment, in consideration of theimage display area on the screen, i.e., in consideration of the shiftand zoom positions of the projection system, a distorted image isdetermined by shape for formation to a liquid crystal light valve.

A-3. Correction of Image Distortion

FIG. 5 is a flowchart showing the procedure of correcting any distortionobserved in an image displayed on a screen. The procedure of FIG. 5 isexecuted by the distortion correction section 430, and is started when acommand is issued for a distortion correction process in response to theuser operation of the operation section 510, for example. Morespecifically, the operation section 510 is provided with a plurality ofcorrection buttons for correcting the shape of images to be projectedfor display. Every time the user operates any of such correctionbuttons, the CPU 400 makes the distortion correction section 430 executethe procedure of FIG. 5.

In step S102, the target display area determination section 432 acquiresthe shift and zoom positions of the projection system 340. More indetail, the target display area determination section 432 makes theshift position detection section 362 detect the shift position of theprojection system 340 so that the resulting detection values (currentvalues) are acquired. The target display area determination section 432also makes the zoom position detection section 364 detect the zoomposition of the projection system 340 so that the resulting detectionvalues (current values) are acquired.

In this embodiment, the projection system adjustment section 350 iscapable of adjusting the shift and zoom positions of the projectionsystem 340 in response to user-issued commands. With this being thecase, instead of the detection values, as the current values of theshift and zoom positions, the control values of the shift and zoompositions provided to the projection system adjustment section 350 maybe acquired.

In step S104, based on the detection values (current values) of theshift and zoom positions of the projection system derived in step S102,the target display area determination section 432 determines a displayarea serving as a target of any image to be displayed on the screen.

FIG. 6 is an illustrative diagram showing a target display area WSt.FIG. 6 also shows a reference display area WSs including therein thetarget display area WSt. The reference display area WSs displays thereinan image when the projection system is changed in shift and zoompositions in an allowable range. Note here that the size of thereference display area WSs is set irrespective of the projection angleof the projector, and is of the size when the tilt angle φ and the panangle θ of the projector are both 0 degree. In this embodiment, thereference display area WSs is ready in advance based on the allowablerange for the shift and zoom positions of the projection system. In stepS104, based on the current values of the shift and zoom positions of theprojection system, a target display area WSt is determined in thereference display area WSs. As is known from this, the reference displayarea WSs is an area including the target display areas corresponding tothe shift and zoom positions in the allowable range of the projectionsystem 340.

As shown in the drawing, the reference display area WSs and the targetdisplay area WSt are both rectangle shaped. The aspect ratio, i.e.,dimension ratio of lateral to vertical, of the reference display areaWSs is dependent on the allowable range of the shift and zoom positionsof the projection system. The aspect ratio of the target display areaWSt is the same as that of the liquid crystal light valve 300, e.g., inthis embodiment, 4:3.

In step S106 of FIG. 5, the reference formation area determinationsection 434 acquires the projection angle of the projector. Inside ofthe projector, the user operation of a plurality of correction buttonsprovided to the operation section 510 is dealt as settings of theprojection angle of the projector PJ with respect to the screen. Forexample, when the user depresses a specific correction button for once,the setting value of the tilt angle φ is increased by a predeterminedangle. That is, in step S106, the reference formation area determinationsection 434 acquires the projection angles θ and φ of FIGS. 2A and 2Bthat are set by the user operation of any corresponding correctionbuttons.

Alternatively, the projection angle of the projector may be acquired byany other techniques. As an example, the projection angles φ and θ maybe acquired based on any characteristics of a projection surface in animage, e.g., based on the shape or angle of the screen or wall surfacein the image. The image here may be the one picked up by an image pickupdevice such as CCD (Charge-Coupled Device) camera equipped in theprojector, for example. Still alternatively, the projector may beprovided with a gravity sensor to directly acquire the projection angleφ.

In step S108, based on the projection angle acquired in step S106, thereference formation area determination section 434 determines areference formation area corresponding to the reference display areaWSs.

FIG. 7 is an illustrative diagram showing the reference formation areaWLs. The reference formation area WLs is formed with a virtual distortedimage for formation on the liquid crystal light valve 300 when arectangular image is displayed in the reference display area WSs of FIG.6. The reference formation area WLs is larger than the liquid crystallight valve 300. That is, in step S108, the reference formation area WLsis determined on a virtual liquid crystal light valve VL.

As already described, the aspect ratio of the reference display area WSsis dependent on the allowable range of the projection system.Accordingly, the shape of the reference formation area WLs is alsodependent on the allowable range of the projection system. The aspectratio of the virtual liquid crystal light valve VL is the same as thatof the reference display area WSs, and is dependent on the allowablerange of the projection system.

In this embodiment, the reference formation area WLs is determined usinga table. More specifically, the reference formation area determinationsection 434 is provided with a table TB, which carries therein aplurality of potential reference formation areas corresponding to aplurality of combinations of the projection angles φ and θ. Based on theprojection angles φ and θ acquired in step S106, one potential referenceformation area is selected as a reference formation area.

The potential reference formation areas stored in the table TB aredetermined by the following transformation equation, i.e., equation 1.

Equation 1

Herein, the xyz coordinate system is the coordinate system of the screenSC (refer to FIGS. 2A and 2B). The coordinates of (x, y, z) are thosebefore transformation in the xyz coordinate system, and the coordinatesof (x′, y′, z′) are those after transformation therein. The XYcoordinate system is that of the virtual liquid crystal light valve VL.

The table TB actually carries therein coordinates of every potentialreference formation area, i.e., their coordinates of points at fourcorners. The coordinates of such four-corner points of the respectivepotential reference formation areas are derived by substituting thefour-corner point coordinates of the reference display area WSs in x andy of the equation 1, and by substituting the distance from the projectorPJ to the reference display area WSs in z of the equation 1.

The values of x, y, and z of the equation 1 are determined as below, forexample. Assumed here is that the liquid crystal light valve 300 is ofXGA (1024 by 768 pixels) in size, and the reference display area WSsafter the projection system is moved in the allowable range is 2048 by1536 pixels in size. When the reference display area WSs is set to thesize of 2048 cm by 1536 cm, the values of x and y are determined for thefour-corner points of the reference display area WSs. Also determined issuch a distance z that can lead to the reference display area WSs havingthe size of 2048 cm by 1536 cm. Alternatively, by measuring the size ofthe reference display area WSs with the distance z set to 1 m, thevalues of x and y may be determined for the four-corner points of thereference display area WSs. In the equation 1, the values of x′ and y′are cancelled to the lowest terms by the value of z′ at the time oftransformation into the two-dimensional XY coordinate system.Accordingly, when the values of x and y are set depending on the valueof z, and when the values of z is set depending on the values of x andy, the shape (and the size) of the reference formation area WLs will bethe same.

In step S110 of FIG. 5, based on the correspondence between thereference display area WSs and the reference formation area WLs, thetarget formation area determination section 436 determines atransformation equation for use for projection transformation.

FIGS. 8A and 8B are illustrative diagrams showing, respectively, thereference display area WSs and the reference formation area WLs. Thereare correspondences between points of P1(x1, y1) to P4(x4, y4) at fourcorners of the reference display area WSs, and points of P1′(X1, Y1) toP′4(X4, Y4) at four corners of the reference formation area WLs.

The transformation equation, i.e., equation 2, is derived based on thecorrespondences of FIGS. 8A and 8B.

Equation 2

In the equation 2, a to h are all a constant. These constants of a to hare derived by solving simultaneous equations (eight equations), i.e.,by substituting the coordinates of the four-corner points P1 to P4 ofthe reference display area WSs in (x, y), and by substituting thefour-corner points P1′ to P4′ of the reference formation area WLs in (X,Y).

Utilizing the transformation equation (equation 2) as a result of stepS110 can derive a point Pk′ (Xk, Yk) in the reference formation area WLscorresponding to any arbitrary point Pk(xk, yk) in the reference displayarea WSs.

In step S112 of FIG. 5, utilizing the transformation equation as aresult of step S110, the target formation area determination section 436determines a target formation area corresponding to the target displayarea WSt.

FIGS. 9A and 9B are illustrative diagrams showing, respectively, thetarget display area WSt and the target formation area WLt. FIG. 9A showsthe target display area WSt in the reference display area WSs. FIG. 9Bshows a target formation area WLt in the reference formation area WLstogether with the liquid crystal light valve 300. When the targetformation area WLt in the liquid crystal light valve 300 of FIG. 9B isformed with a distorted image, a regular image is displayed in thetarget display area WSt of FIG. 9A.

As is known from comparison between FIGS. 9A and 9B, by equalizing thesize of the reference display area WSs and the size of the virtualliquid crystal light valve VL, the positional relationship between thevirtual liquid crystal light valve VL and the actual liquid crystallight valve 300 is the same as that between the reference display areaWSs and the target display area WSt.

In step S114 of FIG. 5, the correction application section 438 correctsoriginal image data in such a manner as to form a distorted image in thetarget formation area WLt on the liquid crystal light valve 300. Theresult derived by such correction is corrected image data.

The correction in step S114 is applied using the transformation equation(equation 2) derived in step S110. More specifically, assumed here isthat the target display area WSt carries therein an original imagerepresented by the original image data, and the target formation areaWLt carries therein a distorted image represented by the corrected imagedata. In accordance with the transformation equation (equation 2), anattention pixel in the original image is determined with itscorresponding pixel in the distorted image. Thus determinedcorresponding pixel is assigned with a pixel value of the attentionpixel. At this time, it is preferable if an interpolation process isexecuted as appropriate.

The corrected image data generated by the distortion correction section430 as such is supplied to the liquid crystal light valve 300 by theimage processing section 420. As a result, the target display area WSton the screen displays a regular image.

As described in the foregoing, in this embodiment, exemplified is theprojector in which the projection system can be changed in position. Inthis embodiment, utilizing the transformation equation (equation 2)determined based on the relationship between the reference display areaWSs and the reference formation area WLs, the target formation area WLtcorresponding to the target display area WSt is determined. The originalimage data is then so corrected that the target formation area WLt isformed with a distorted image, and the corrected image data isgenerated. That is, in this embodiment, in consideration of the targetdisplay area WSt determined based on the shift and zoom positions of theprojection system, the corrected image data is generated so that anydistortion observed in images displayed on the screen can be correctedwith accuracy.

A-4. Modified Example of First Embodiment

Although the target formation area WLt is fit in the liquid crystallight valve 300 in FIG. 9B, this is not always the case. Described hereis the process of a case with no fit. For comparison, however, describedfirst is the process in a case where the target formation area fits inthe liquid crystal light valve 300. For the sake of description,exemplified below is a case where the pan angle θ is 0 degree (refer toFIGS. 2A and 2B).

FIGS. 10A and 10B are each an illustrative diagram showing the processin a case where a target formation area fits in a liquid crystal lightvalve. FIG. 10A shows a target display area WSt1 in a reference displayarea WSs1, and FIG. 10B shows a target formation area WLt1 in areference formation area WLs1.

In FIG. 10B, the liquid crystal light valve 300 is including therein thetarget formation area WLt1. Therefore, as described in the firstembodiment, by forming a distorted image in the target formation areaWLt1 of the liquid crystal light valve 300, the target display area WSt1of FIG. 10A displays a regular image.

Note that, in FIG. 10A, the area indicated by dashed lines outside ofthe reference display area WSs1 denotes an image display area on thescreen when a rectangular image is displayed on the virtual liquidcrystal light valve VL1. The image on the screen is expanding towardupward.

FIGS. 11A-1 to 11B-2 are illustrative diagram each showing a firstprocess in a case where a target formation area does not fit in a liquidcrystal light valve. FIGS. 11A-1 and 11A-2 show target display areasWSt2 and WSt2′ in the reference display areas WSs1 and WSs1′,respectively. FIGS. 11B-1 and 11B-2 show target formation areas WLt2 andWLt2′ in the reference formation areas WLs2 and WLs1′, respectively.

As is known from comparison between FIG. 10A and 11A-1, the targetdisplay area WSt2′ of FIG. 11A-1 is located upper than the targetdisplay area WSt2 of FIG. 10A. That is, FIGS. 11A-1 and 10A show casesof varying shift position of the projection system 340. In these cases,as shown in FIG. 11B-1, the liquid crystal light valve 300 is notincluding the lower side portion of the target formation area WLt2.Therefore, if the target formation area WLt2 in the liquid crystal lightvalve 300 is formed with a distorted image, the target display area WSt2of FIG. 11A-1 does not display a perfect image but an imperfect imagehaving no lower side portion.

In consideration thereof, in the first process, as shown in FIG. 11B-2,the reference formation area WLs1′ in the virtual liquid crystal lightvalve VL1 is changed in position toward upward. In other words, thereference formation area WLs1′ is changed in position with respect tothe liquid crystal light valve 300. As a result, the liquid crystallight valve 300 includes therein the target formation area WLt2′ so thatthe target display area WSt2′ of FIG. 11A-2 is displayed with a perfectimage. Note that, because the reference formation area WLs1′ of FIG.11B-2 is changed in position toward upward, as shown in FIG. 11A-2, theposition of the reference display area WSs1′ is changed to come upperthan the reference display area WSs1 of FIG. 11A-1. As a result, asshown in FIG. 11A-2, the position of the target display area SWt2′ ischanged to come upper than the target display area WSt2 of FIG. 11A-1.

In FIG. 11B-2, the reference formation area WLs1′ is changed inposition, and the shape thereof is different from that of the referenceformation area WLs1 of FIG. 11A-2. More specifically, the shape of thereference formation area WLs1′ of FIG. 11B-2 is derived by subjectingthe reference display area WSs1′ of FIG. 11A-2 to projectiontransformation utilizing the transformation equation (equation 2) as aresult of step S110. The shape of the target formation area WLt2′ ofFIG. 11B-2 is derived by subjecting the target display area WSt2′ ofFIG. 11A-2 to projection transformation utilizing the transformationequation (equation 2) as a result of step S110.

As is known from the above, at the time of the first process, actually,the target display area WSt2 may be changed in position so as to makethe target formation area WLt2′ corresponding to the resulting targetdisplay area WSt2′ fit in the liquid crystal light valve 300. There isthus no need to derive the reference formation area WLs1′ after thechange. That is, in the first process, in step S112, when determiningthat the target formation area WLt2 does not fit in the liquid crystallight valve 300, the target formation area determination section 436changes the position of the target display area WSt2 toward upward.Utilizing the transformation equation (equation 2) derived in step S110based on the relationship between the reference display area WSs1 andthe reference formation area WLs1, the target formation areadetermination section 436 then determines a new target formation areacorresponding to the target display area WSt2 after the position change.

Herein, through comparison between the coordinates of the liquid crystallight valve 300 in the XY coordinate system and the coordinates of thetarget formation area, it can be determined whether or not the targetformation area fits in the liquid crystal light valve 300.

FIGS. 12A-1 to 12B-2 are all an illustrative diagram showing a secondprocess in a case where a target formation area does not fit in a liquidcrystal light valve. FIGS. 12A-1 and 12A-2 are both showing the targetdisplay area WSt2 in the reference display area WSs1, and FIGS. 12B-1and 12B-2 are both showing the target formation area WLt2 in thereference formation area WLs1. FIGS. 12A-1 and 12B-1 are the same asFIGS. 11A-1 and 11B-1.

As described by referring to FIGS. 11A-1 and 11B-1, in FIG. 12B-1, theliquid crystal light valve 300 is not including the lower side portionof the target formation area WLt2. Therefore, if the target formationarea WLt2 in the liquid crystal light valve 300 is formed with adistorted image, the target display area WSt2 of FIG. 12A-1 does notdisplay a perfect image but an imperfect image having no lower sideportion.

In consideration thereof, in the second process, as shown in FIG. 12B-2,the target formation area WLt2 in the liquid crystal light valve 300 ischanged in position toward upward. In other words, the liquid crystallight valve 300 in the virtual liquid crystal light valve VL1 is changedin position toward downward. As a result, the liquid crystal light valve300 includes therein the target formation area WLt2. However, changingthe position of the target formation area WLt2 in the liquid crystallight valve 300 is not enough, and the target display area isresultantly changed in position toward upward. Therefore, in the secondprocess, by moving the projection system in shift position towarddownward, a regular image is displayed in the target display area WSt2of FIG. 12B-2.

Unlike FIG. 11B-2, in FIG. 11B-2, the reference formation area WLs1 isnot changed in position, and the target formation areas WLt2 of FIGS.12B-1 and 12B-2 share the same shape. Accordingly, at the time of thesecond process, unlike the time of the first process, there is no needto derive again the target formation area. That is, in the secondprocess, in step S112, when determining that the target formation areaWLt2 does not fit in the liquid crystal light valve 300, the targetformation area determination section 436 changes the position of thetarget display area WLt2 in the liquid crystal light valve 300 towardupward. The target formation area determination section 436 also makesthe projection system adjustment section 350 change the shift positionof the projection system 340 toward downward. As is known from this, theprojection system adjustment section 350 in the second process isequivalent to an actuator in the invention.

B. Second Embodiment

B-1. Configuration of Projector

FIG. 13 is a block diagram showing the configuration of a projector PJBin a second embodiment. FIG. 13 is almost the same as FIG. 1 except foran image processing section 420B, more specifically, a distortioncorrection section 430B. In this embodiment, a setting memory 440 isprovided as alternatives to the projection system adjustment section350, the shift position detection section 362, and the zoom positiondetection section 364 in FIG. 1.

The setting memory 440 is storing setting values, indicating theposition and magnification of a distorted image for formation on theliquid crystal light valve 300. The position and magnification of adistorted image for formation on the liquid crystal light valve 300specify the position and magnification of a regular image for display onthe screen. The setting value for the position is represented by themovement direction and amount from any predetermined position of adistorted image in the liquid crystal light valve. In this embodiment,as the setting value for the magnification, a value smaller than 1 ispresumably set. The position and magnification of the distorted imageare set through user operation of the operation section 510, and theresults are stored in the setting memory 440.

B-2. Image Distortion on Screen Display

When low-angle image projection is made onto a screen, if a distortedimage is first formed on a liquid crystal light valve for the purpose ofdisplaying a regular image on the screen, and if a formation area forthe resulting distorted image is then changed, i.e., if the resultingdistorted image is changed in position and magnification in the liquidcrystal light valve, the resulting image on the screen is distorted.This is caused because the image display area on the screen is changedas the formation area is changed for the distorted image in the liquidcrystal light valve.

FIGS. 14A and 14B are illustrative diagrams showing, respectively, animage formed on a liquid crystal light valve, and an image displayed onthe screen depending on the position of the image. When the liquidcrystal light valve 300 is formed, at its center portion, with atrapezoidal distorted image LP3 of FIG. 14A, the screen displays animage SP3 of FIG. 14B. Thereafter, without changing the shape of thedistorted image LP3 formed in the liquid crystal light valve 300, whendistorted images LP3 a to PL3 d are formed at each different position inthe liquid crystal light valve 300 as shown in FIG. 14A, the distortedimages SP3 a to SP3 d are changed in position on the screen as shown inFIG. 14B. As a result, the images SP3 a to SP3 d are all changed inshape. For example, if the liquid crystal light valve 300 is formed withthe distorted image LP3 a on the right side, the screen displays thedistorted image SP3 a extending toward right.

FIGS. 15A and 15B are illustrative diagrams showing, respectively, animage formed on a liquid crystal light valve, and an image displayed onthe screen depending on the magnification of the image. When the liquidcrystal light valve 300 is formed with a trapezoidal distorted image LP4with the intermediate magnification of FIG. 15A, the screen displays animage SP4 of FIG. 15B. Thereafter, if distorted images LP4 a and LP4 bare formed with each different magnification (size) as shown in FIG. 15Awhile the distorted image LP4 formed in the liquid crystal light valve300 being similar in shape, the images SP4 a and SP4 b are changed insize for display on the screen as shown in FIG. 15B. As a result, theimages SP4 a and SP4 b are both changed in shape. For example, theliquid crystal light valve 300 is formed with a distorted image LP4 bwith the relatively-high magnification, the screen displays the imageSP4 b expanding toward upward.

As described in the foregoing, when the image display area is changed onthe screen by changing the position and magnification of a distortedimage to be formed on the liquid crystal light valve 300, the image tobe displayed on the screen is changed in shape.

The issue here is that, when the distorted image is determined by shapefor formation on the liquid crystal light valve 300, no considerationhas been given to the position and magnification of the distorted image.In other words, previously, the image display area on the screen has notbeen considered. Therefore, it has been difficult to display on thescreen rectangular images (regular images) of a correct aspect ratio.

In consideration thereof, in this embodiment, in consideration of theimage display area on the screen, i.e., the position and magnificationof a distorted image to be formed on a liquid crystal light valve, adistorted image is determined by shape for formation on the liquidcrystal light valve.

B-3. Correction of Image Distortion

FIG. 16 is a flowchart showing the procedure of correcting anydistortion observed in an image displayed on a screen. In a similarmanner to the first embodiment (FIG. 5), the procedure of FIG. 16 isexecuted by the distortion correction section 430B, and is started whena command is issued for a distortion correction process in response tothe user operation of the operation section 510, for example.

In step S202, a target display area determination section 432B acquiresthe position and magnification of a distorted image to be formed on aliquid crystal light valve. More in detail, the target display areadetermination section 432B reads the setting value (current value)showing the formation position of a distorted image stored in thesetting memory 440, and reads the setting value (current value) showingthe formation magnification of the distorted image.

In step S204, similarly to step S104 of FIG. 5, based on the settingvalues (current values) for the position and magnification of thedistorted image acquired in step S102, the target display areadetermination section 432B determines a display area, i.e., targetdisplay area, serving as a target of any image to be displayed on thescreen.

FIG. 17 is an illustrative diagram showing a target display area WSBt.FIG. 17 also shows a reference display area WSBs including therein thetarget display area WSBt. The reference display area WSBs displaystherein an image when the distorted image is changed in position andmagnification in the liquid crystal light vale in a possible range. Thesize of the reference display area WSBs is set irrespective of theprojection angle of the projector, and is of the size when the tiltangle φ and the pan angle θ of the projector are both 0 degree. In thisembodiment, the reference display area WSBs is ready in advance based onthe possible range for the position and magnification of the distortedimage. In step S204, based on the current values of the position andmagnification of the distorted image in the liquid crystal light valve,the target display area WSBt is determined in the reference display areaWSBs. As is known from this, the reference display area WSBs is an areaincluding the target display areas corresponding to the positions andmagnifications in the possible range of the distorted image to be formedin the liquid crystal light valve 300.

The reference display area WSBs and the target display area WSBt areboth rectangle shaped. The aspect ratio of the reference display areaWSBs, and the aspect ratio of the target display area WSt are the sameas that of the liquid crystal light valve 300, e.g., in this embodiment,4:3.

In step S206 of FIG. 16, similarly to step S106 of FIG. 5, the referenceformation area determination section 434B acquires the projection angleof the projector.

In step S208, similarly to step S108 of FIG. 5, the reference formationarea determination section 434B determines a reference formation areacorresponding to the reference display area WSs based on the projectionangle acquired in step S206.

FIG. 18 is an illustrative diagram showing a reference formation areaWLBs. The reference formation area WLBs is formed with a virtualdistorted image to be formed on a liquid crystal light valve when thereference display area WSBs of FIG. 17 is formed with a rectangularimage (regular image) of a correct aspect ratio. Note in this embodimentthat, unlike the first embodiment, the reference formation area WLBs issmaller than the liquid crystal light valve 300. That is, in step S208,the reference formation area WLBs is formed on the actual liquid crystallight valve 300. Also in this embodiment, similarly to the firstembodiment, the reference formation area WLBs is determined using atable TBB provided to the reference formation area determination section434B.

In step S210 (FIG. 16), similarly to step S110 of FIG. 5, a targetformation area determination section 436B determines a transformationequation for projection transformation based on the correspondencebetween the reference display area WSBs and the reference formation areaWLBs. The transformation equation (refer to equation 2) is derived usingcoordinates of four-corner points of the reference display area WSBs andthose of the reference formation area WLBs.

In step S212, similarly to step S112 of FIG. 5, the target formationarea determination section 436B determines a target formation areacorresponding to the target display area WSBt using the transformationequation derived in step S210.

FIGS. 19A and l9B are illustrative diagrams showing, respectively, thetarget display area WSBt and the target formation area WLBt. FIG. 19Ashows the target display area WSBt in the reference display area WSBs,and FIG. 19B shows the target formation area WLBt in the referenceformation area WLBs together with the liquid crystal light valve 300.When the target formation area WLBt in the liquid crystal light valve300 of FIG. 19B is formed with a distorted image, a regular image isdisplayed in the target display area WSBt of FIG. 19A.

In step S214 of FIG. 16, similarly to step S114 of FIG. 5, a correctionapplication section 438B may correct original image data in such amanner that the target formation area WLBt on the liquid crystal lightvalve 300 is formed with a distorted image. As a result, generated iscorrected image data.

The corrected image data generated by the distortion correction section430B is supplied to the liquid crystal light valve 300 by the imageprocessing section 420B. As a result, the target display area WSBt onthe screen displays a regular image.

As described in the foregoing, in this embodiment, exemplified is theprojector in which the position and magnification can be changed for adistorted image to be formed on the liquid crystal light valve. In thisembodiment, utilizing the transformation equation (equation 2)determined based on the relationship between the reference display areaWSBs and the reference formation area WLBs, the target formation areaWLBt corresponding to the target display area WSBt is determined. Theoriginal image data is then so corrected that the target formation areaWLBt is formed with a distorted image, and the correct image data isgenerated. That is, in this embodiment, in consideration of the targetdisplay area WSt determined based on the position and magnification ofthe distorted image in the liquid crystal light valve, the correctedimage data is generated so that any distortion observed in imagesdisplayed on the screen can be corrected with accuracy.

In the modified example of the first embodiment, described is theprocess in a case where a target formation area does not fit in theliquid crystal light valve 300. In this embodiment, because the actualliquid crystal light valve 300 is used as an alternative to the virtualliquid crystal light valve VL of the first embodiment, such a problem isnot caused.

The foregoing description is in all aspects illustrative and notrestrictive, and it is understood that numerous other modifications andvariations can be devised without departing from the scope of theinvention. For example, the following modifications are possible.

1. A target display area is determined based on the shift and zoompositions of the projection system 340 in the first embodiment.Alternatively, as in the second embodiment, the target formation areamay be determined based on the position and magnification of a distortedimage to be formatted on the liquid crystal light valve 300.

With this being the case, a reference display area may be set to thearea WSs similar to the first embodiment. The target display area may beset to a part of the area WSt in the first embodiment based on the shiftand zoom positions of a projection system, and the position andmagnification of a distorted image. The reference formation area may beset to the area WLs similar to the first embodiment. The targetformation area may be set to a part of the area WLt in the firstembodiment based on the relationship between the reference display areaand the reference formation area.

2. The target formation area WLt is derived in step S112 in the firstembodiment, but is not necessarily derived independently. That is,utilizing the transformation equation (equation 2) in step S114, thecorrection application section 438B may generate corrected data bycorrecting original image data in such a manner that an area (targetformation area) in the liquid crystal light valve corresponding to thetarget display area is formed with a distorted image. Note here that ifthe target formation area determination section 436 is set to deriveindependently the target formation area WLt, as described in themodified example of the first embodiment, there is an advantage ofmaking a determination whether or not the target formation area fits inthe liquid crystal light valve 300 before the corrected image data isgenerated. Note here that, also in the second embodiment, similarly tothe above, the target formation area WLBt is not necessarily derivedindependently.

The correction application section may correct any given original imagedata in such a manner that a distorted image is formed in a targetformation area corresponding to a target display area that is determinedgenerally based on the relationship between a reference display area anda reference formation area, and may generate corrected image data forsupply to the image formation section.

3. In the above embodiments, the projectors PJ and PJB are provided withthe distortion correction sections 430 and 430B, respectively, and areequivalent to the image processing device and the projector in theinvention. This is not surely restrictive, and the distortion correctionsection may be provided not to a projector but to a personal computer.With this being the case, the computer is equivalent to the imageprocessing device of the invention.

4. In the above embodiments, the projectors may be provided with amicromirror-type light modulator such as DMD (Digital MicromirrorDevice) (trademark of Texas Instruments) as an alternative to a liquidcrystal light valve. Alternatively, the projector may be provided with ahigh-intensity CRT (Cathode-Ray Tube), a plasma display panel, anelectroluminescent display panel, a light-emitting diode display panel,a field emission display panel, and the like. As such, the imageformation section is exemplified by an involuntary or voluntary emissiondevice.

5. In the above embodiments, the configuration implemented by hardwaremay be replaced by software, or the configuration implemented bysoftware may be replaced by hardware.

1. An image processing device for a projector including an imageformation section that emits light of an image, and a projection systemthat projects the emitted light onto a projection surface, comprising: atarget display area determination section that determines, in a displayarea serving as a reference on the projection surface, based on acurrent value of a parameter, any of target display areas set for valuespossibly taken by the parameter within an allowable range to be targetedon a distortion-free image for display on the projection surface; areference formation area determination section that determines,corresponding to the reference display area, based on information abouta projection angle of the projector with respect to the projectionsurface, a reference formation area to be formed with a virtualdistorted image that is supposed to be formed in the image formationsection when the distortion-free image is displayed in the referencedisplay area; and a correction application section that generatescorrected image data for supply to the image formation section bycorrecting any provided original image data to form a target distortedimage in a target formation area, which corresponds to the targetdisplay area as is defined by a relationship between the referencedisplay area and the reference formation area, and is formed with thetarget distorted image that is supposed to be formed in the imageformation section when the distortion-free image is displayed in thereference display area.
 2. The image processing device according toclaim 1, wherein the parameter includes a shift position of theprojection system indicating a layout of the projection system in adirection orthogonal to an axis passing through a center of an imageformation surface of the image formation section.
 3. The imageprocessing device according to claim 1, wherein the parameter includes azoom position of the projection system indicating a layout of theprojection system in a direction parallel to an axis passing through acenter of an image formation surface of the image formation section. 4.The image processing device according to claim 1, further comprising atarget formation area determination section that determines the targetformation area corresponding to the target display area based on therelationship between the reference display area and the referenceformation area.
 5. The image processing device according to claim 4,wherein when the target formation area does not fit in the imageformation section, the target formation area determination sectionchanges a position of the target display area to ensure a fit in theimage formation section, and based on the relationship between thereference display area and the reference formation area, newlydetermines the target formation area corresponding to the target displayarea after the position change.
 6. The image processing device accordingto claim 4, wherein the projector further includes an actuator forchanging a shift position of the projection system, and when the targetformation area does not fit in the image formation section, the targetformation area determination section changes a position of the targetformation area to ensure a fit in the image formation section, and makesthe actuator change the shift position of the projection system toensure an image display in the target display area.
 7. The imageprocessing device according to claim 1, wherein the parameter includes aposition of the target distorted image that is supposed to be formed inthe image formation section.
 8. The image processing device according toclaim 1, wherein the parameter includes a magnification of the targetdistorted image that is supposed to be formed in the image formationsection.
 9. A projector, comprising: the image processing device ofclaim 1; the image formation section; and the projection system.
 10. Animage processing method for a projector including an image formationsection that emits light of an image, and a projection system thatprojects the emitted light onto a projection surface, comprising:determining, in a display area serving as a reference on the projectionsurface, based on a current value of a parameter, any of target displayareas set for values possibly taken by the parameter within an allowablerange to be targeted on a distortion-free image for display on theprojection surface; determining, corresponding to the reference displayarea, based on information about a projection angle of the projectorwith respect to the projection surface, a reference formation area to beformed with a virtual distorted image that is supposed to be formed inthe image formation section when the distortion-free image is displayedin the reference display area; and generating corrected image data forsupply to the image formation section by correcting any providedoriginal image data to form a target distorted image in a targetformation area, which corresponds to the target display area as isdefined by a relationship between the reference display area and thereference formation area, and is formed with the target distorted imagethat is supposed to be formed in the image formation section when thedistortion-free image is displayed in the target display area.
 11. Acomputer readable storage medium storing a program for image processingfor a projector including an image formation section that emits light ofan image, and a projection system that projects the emitted light onto aprojection surface, the program causing a computer to execute:determining, in a display area serving as a reference on the projectionsurface, based on a current value of a parameter, any of target displayareas set for values possibly taken by the parameter within an allowablerange to be targeted on a distortion-free image for display on theprojection surface; determining, corresponding to the reference displayarea, based on information about a projection angle of the projectorwith respect to the projection surface, a reference formation area to beformed with a virtual distorted image that is supposed to be formed inthe image formation section when the distortion-free image is displayedin the reference display area; and generating corrected image data forsupply to the image formation section by correcting any providedoriginal image data to form a target distorted image in a targetformation area, which corresponds to the target display area as isdefined by a relationship between the reference display area and thereference formation area, and is formed with the target distorted imagethat is supposed to be formed in the image formation section when thedistortion-free image is displayed in the target display area.